Why intermolecular bonds “make” gluten strong
Gluten is a protein network that emerges when gliadins and glutenins are hydrated and subjected to mechanical energy (mixing/kneading) or thermal energy (heating). Its “strength” (tenacity/elasticity and ability to withstand stress) depends on two families of interactions:
1 – Covalent disulfide bonds (S–S).
These are the most “structural” cross-links. In glutenins (especially HMW-GS and LMW-GS), intermolecular disulfide bonds build polymers (often referred to as GMP / glutenin macropolymer) that provide the elastic backbone of the network.
2 – Non-covalent interactions (hydrophobic, hydrogen bonds, ionic interactions).
They are weaker but extremely numerous and “modulate” the network: they contribute to cohesion, viscosity, reorganization, and the response to hydration/temperature/solvents. Many studies show that changes in secondary structure and non-covalent interactions accompany (and sometimes amplify) the effects of disulfide bonds.
A key point:
the network is not static. During processing, thiol–disulfide exchange reactions (–SH/–S–S–) occur that remodel network connectivity: more opportunities to form/reorganize S–S bonds → generally a “stronger” and/or more resilient network.
Practical implications for dough
From an operational standpoint, gluten strength does not depend only on the genetic potential of the flour, but also on how the system is “set up” to express and organize its intermolecular bonds.
Adequate hydration:
Water acts as a plasticizer and allows proteins to move, interact, and realign. Hydration levels that are too low limit network formation; higher hydration promotes molecular mobility and bond reorganization, making gluten more extensible.
Mixing energy:
Mechanical action facilitates contact between protein chains and accelerates thiol–disulfide exchange reactions. Insufficient mixing leads to an incomplete network; excessive energy, on the other hand, can cause bond breakage and excessive reorganization, with a loss of structure.
Resting time:
Rest phases (autolyse, bulk fermentation) allow non-covalent interactions and disulfide bonds to redistribute toward more stable configurations, improving the balance between elasticity and extensibility.
Chemical conditions:
pH, salts, and the presence of oxidizing or reducing agents directly influence the equilibrium between –SH groups and –S–S– bridges, thereby modulating cross-link density within the network.
In summary, mixing practices do not create new proteins, but determine how effectively the available intermolecular bonds are organized, translating the flour’s potential into observable rheological properties.
Studies and key points
1) Basic chemical framework: what we know about disulfides and network architecture
Wieser, H. (2023) – Chemistry of wheat gluten proteins: Qualitative composition
DOI: 10.1002/cche.10572 (Wiley Online Library)
Key points
A modern review of composition and the roles of fractions (gliadins vs. glutenins) and of disulfide bonds in linking subunits and (under certain conditions) incorporating some gliadins into the polymeric fraction.
Useful as a “theoretical introduction” and for terminology (HMW/LMW, polymers, reactive cysteines).
2) Industrial/processing “mechanism”: why S–S bonds and –SH/–S–S– exchange are emphasized
Domenek et al. (2010) – Molecular Basis of Processing Wheat Gluten toward Biobased Materials
DOI: 10.1021/bm100008p (ACS Publications)
Key points
Clearly explains that network formation is mainly attributed to intermolecular disulfide bond formation plus thiol/disulfide exchange during processing (shear, heat, redox conditions).
Although oriented toward materials/biopolymers, it is excellent for understanding the “physics + chemistry” of gluten as a network.
3) Direct identification of disulfides: where they are and who links to whom
Lutz, E. et al. (2012) – Identification of Disulfide Bonds in Wheat Gluten Proteins… (LC-MS with ETD/CID)
DOI: 10.1021/jf204973u (ACS Publications)
Key points
“Hard evidence” approach: mapping disulfide bonds in gluten proteins via LC-MS.
Useful to move from “it is thought that…” to “these specific S–S bridges have been observed,” and to reason about how many cysteines are actually available for cross-linking.
4) Polymer composition and the role of “odd-cysteine gliadins” (chain terminators)
Vensel, W.H. et al. (2014) – Protein composition of wheat gluten polymer fractions… (Proteome Science, open access)
DOI: 10.1186/1477-5956-12-8 (Springer Nature)
Key points
They separate polymeric fractions (EPP/UPP) and show that some gliadins with an odd number of cysteines appear in the polymeric fraction.
Supports the idea that certain gliadins can act as “chain terminators”: they enter the polymer via S–S bonds but may limit chain extension/architecture → impact on polymer size and thus properties.
5) Isolated gluten/glutenin/gliadin: disulfides + non-covalent interactions and how they change (fraction-level measurements)
Wang, P. et al. (2014) – Effect of frozen storage on physico-chemistry of wheat gluten proteins: studies on gluten-, glutenin- and gliadin-rich fractions (Food Hydrocolloids)
DOI: 10.1016/j.foodhyd.2014.01.009 (ScienceDirect)
Key points
Useful because it works on enriched fractions (gluten/glutenin/gliadin) and monitors SE-HPLC (GMP), thiols, SDS-PAGE, FTIR/CD.
Shows that modifications in the glutenin fraction (GMP/polymers) are decisive for rheological changes, and that non-covalent interactions also change together with the network.
6) Disulfide dynamics as a functional “lever”
Ooms, N. et al. (2018) – The impact of disulfide bond dynamics in wheat gluten protein… (Food Chemistry)
DOI: 10.1016/j.foodchem.2017.09.007 (ScienceDirect)
Key points
Focuses on disulfide dynamics (not just “how many,” but “how much they reorganize”) and links this to macrostructural product properties.
A clear example of “S–S bridge chemistry → network architecture → properties.”
7) Broad characterization of vital wheat gluten (many samples) with network-structure proxies
Schopf, M. et al. (2021) – Fundamental characterization of wheat gluten (European Food Research and Technology)
DOI: 10.1007/s00217-020-03680-z (ScienceDirect)
Key points
Analyzes many vital wheat gluten samples and uses GP-HPLC/extractions (SDS-soluble, GMP) plus other measurements to link composition/solubility/molecular distribution to functional characteristics.
Useful for “classifying” isolated glutens via parameters reflecting degree of cross-linking (e.g., GMP fraction, extractable/non-extractable fractions).
8) Manipulating –SH / –S–S– and observing the effect (chemical modification of gluten)
Li, H. et al. (2019) – Effect of amino and thiol groups of wheat gluten… (Journal of Food Science and Technology)
DOI: 10.1007/s13197-019-03688-8 (bio-protocol.org)
Key points
Uses modifications affecting thiol/disulfide groups and shows that reducing/altering these functions worsens certain food-system performances (here, noodles), consistent with the structural role of S–S bonds.
Not “pure isolated gluten without matrix,” but useful as functional proof: modify thiols → behavior changes.
9) Broad proteomic identification of gluten components (context for “who is inside”)
Rombouts, I. et al. (2013) – Improved identification of wheat gluten proteins… (Scientific Reports)
DOI: 10.1038/srep02279 (Nature)
Key points
Improves identification of gluten proteins (useful when linking variants/subunits to network properties).
Good methodological support if you want to correlate “protein composition” with bonding capacity (available cysteines, etc.).
Se vuoi, posso anche aiutarti a rifinire il testo in inglese in uno stile più divulgativo o più accademico (ad es. per una review o un capitolo di libro).
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